THE DEVELOP3EEXT OF LAMELLIBRANCHS. 



313 



When a perfectly ripe female is found, it should be set 

 aside and the search continued for a male. When a drop 

 of the milky fluid from a ripe male is mixed with a little 

 sea-water and examined with a magnifying power of one 

 hundred diameters, it is seen at a glance to be quite dif- 

 ferent from the fluid of a female. There are no large 

 bodies like the eggs, but the fluid is filled with innumer- 

 able numbers of minute granules (Fig. 157), w^hich are so 

 small that the}' are barely visible when magnified one 

 hundred diametei*s. They are not unifomily distributed, 

 but are much more numerous at some points than at 

 others, and for this reason the fluid has a cloudy or curdled 

 appearance. By selecting a place where the gi-anules are 

 few and pretty well scattered, very careful watching will 

 show that each of them has a lively dancing motion, and 

 examination with a power of 

 five hundred diameters will 

 show that each of them is tad- 

 pole-shaped (Fig. 158), and 

 consists of a small, oval, shaiply 

 defined "head"' and a long, 

 delicate "tail," by the lashing 

 of which the dancing is pro- 

 duced. 



Fig. 15". — Ripe seminal fluid, mag- 

 nified one hmidred diameters. 



Fig. 157 



It is more difficult to decide whether the male cells are 

 perfectly ripe than it is to decide in the case of the eggs. 

 With a magnifying power of five hundred diameters, each 

 "head" should have a clear, well-marked outline, and 

 they should be ver\' uniform in size and separated from 

 each other, as in Fiff. 158. Under very favorable circum- 



